The present invention relates to a gas-shielded arc welding apparatus for rails, shape steel, etc., and more particularly to its gas shield structure and the automatic and high-quality welding of rails and the like.
In conventional gas-shielded arc welding apparatus of this type, the gas shield structures are so designed that the forward end of a welding nozzle is covered with a tubular shielding gas jet or shielding gas jets are provided at either side or each side of a long and slender welding nozzle.
The former is inefficient since the welding torch is increased in diameter and the groove width must be increased in the case of multi-layer welding of thick plates. Also, while the latter can attain the flattening of the portion comprising the welding nozzle and the shielding gas jets and hence decrease the groove width, it is not suitable, due to the impedimental effect of its gas jets, for such welding processes as the electrogas welding in which the weld zone is enclosed by backing plates. Moreover, the two gas shielding structures are disadvantageous in that each of them provides a localized shielding of the welding arc and the molten metal thus causing the danger of entraining the outside air and tending to cause welding defects such as blow holes.
Also, the automatic welding of rails by the conventional arc welding methods has been difficult due to the complicated cross-sectional shapes of the rails and the rails have been generally welded manually by the enclosed arc welding process. In the enclosed arc welding process, the base portions of rail ends opposed through a gap of about 17 mm and the rail sides are enclosed with copper blocks and the rails are welded manually in the flat position by using a covered arc welding electrode of the low hydrogen type.
The above-mentioned enclosed arc welding process is disadvantageous in that due to the manual welding, the good or bad of welding quality is dependent on the skill of the operator and the weld time is comparatively long thus binding the operator to the work during the welding operation.